Japanese Prime Minister Junichiro Koizumi says he will push ahead with plans to privatize Japan's postal service, despite growing resistance from some members of his ruling party.

With more than $3 trillion in deposits and insurance assets, Japan Post is the world's biggest bank, and its privatization is the main pillar of the prime minister's controversial economic reform program.

As a new session of Parliament opened Friday, Mr. Koizumi told the lawmakers he intends to split the postal service's mail delivery, insurance and savings systems into four separate businesses.

Many conservative lawmakers in the ruling Liberal Democratic Party oppose privatization, in part because this could lead to closure of small post offices in rural areas, a traditional stronghold of the party.